1. Field of the Invention
This invention relates to a gas fired cooking and heating apparatus and, in particular, to a convection oven which uses forced convection currents for uniform and efficient cooking in an economy of space.
2. Description of the Prior Art
Convection ovens which circulate convection currents within the cooking chamber or oven cavity have been well known for many years. Typically, the heat source is disposed below the oven cavity within an oven housing and the hot convection currents are continually introduced into the oven cavity by a fan.
Clearly, a most efficient convection cooking will occur when the food product is baked in uniform currents of constant or nearly constant temperature so that hot spots or cold spots will be avoided as the food is cooking.
In order to facilitate uniform cooking, U.S. Pat. Nos. 4,395,233 and 4,516,012, assigned to the Assignee of this invention, describe a dual flow oven wherein heated air from a gas burner is continually admitted into the oven cavity where it is mixed with recirculated air from within the cavity and circulated around the food to be cooked. This dual flow capability is achieved by the use of a single, special purpose fan wherein heated air from the burner is drawn into the back of the fan, air from within the oven cavity is drawn axially into the front of the fan, and the two currents are expelled radially whereby they mix in a plenum chamber and then circulate throughout the oven cavity, around the food to be cooked, on a continual basis. The fan utilized in such patents is a squirrel cage type fan wherein a plate divides the fan blades, the plate being disposed perpendicular to the axis of rotation and midway between the front and back edges of the fan blades. Radially downstream of the fan, a partition is provided along the adjacent oven wall which receives the currents expelled from the fan, causing the currents to mix, and then expels them to circulate throughout the oven cavity.
The ability to draw in heated air from the burner and air from within the oven cavity, simultaneously, axially, is achieved by, as noted above, a fan which consists of basically two sets of coaxially mounted impeller blades positioned on either side of a rotating centrally disposed circular plate. The fan provides for the forced intake of the two air streams, one flowing along the fan axis in a first direction and a second air stream flowing along the fan axis in an opposite direction, but both moving inwardly toward the center plate. In this manner the fan provides intake force for both the heated air stream from the burner and the recirculated airflow from within the heating compartment and further provides for mixing of same.
The dual flow fan is located in the heating compartment positioned between one of the walls of the heating compartment and a divider panel spaced therefrom which is provided with a central aperture for allowing the recirculated airflow to enter the dual flow fan from within the heating compartment. An aperture is provided behind the fan for admission of the heated airflow from the burner.
Prior art configurations have been found to restrict the working height of the oven cavity space which in turn limits the rack holding capacity. Specifically, the burner is typically in a chamber located extending laterally across the bottom of the oven cavity, and spaced therebelow whereby air can be taken into the oven in the space between the external housing and the oven cavity, circulated around the burner to be heated, and then directed upwardly for entry into the oven. This, in effect, then requires a substantial space between the oven cavity and the housing for location of the burner and for circulation of air to be heated around the burner.
In certain oven designs, the heated air from the burner is also circulated around the bottom, sides, and top of the oven cavity before being admitted thereinto. In such designs, a substantial air space must also be left between the oven cavity and the sides and top of the housing. This further dramatically reduces the interior rack space.
In most commercial environments, however, the space available within which to locate an oven is limited. The configuration of the external housing then is relatively fixed and it is obviously desirable to maximize the internal rack space within the oven cavity while maintaining an efficient heating capability. In the case of convection ovens then this would require minimizing air space between the external housing and the oven cavity walls.
An alternate oven design is provided in U.S. Pat. No. 4,928,663. In this device, a specially designed fan is located at the back of the oven compartment adjacent slots which admit heated air from the burner into the back of the fan. Air from within the oven cavity is drawn into the front of the fan, axially, and the combined currents are expelled by the fan, radially, to be circulated within the oven cavity. In this design, openings are provided in a plate located across the back face of the fan, which openings are registered on slots disposed in the wall above and below the rotational axis of the fan. The opposite face of the fan, facing the oven cavity, is open. Burners located below the oven cavity and within the exterior housing extend across the bottom and air is continually taken into the oven cavity circulated around the exterior of the oven cavity along the sides and top thereof to be directed through the slots in the back wall for entry into the fan. In this way, the heated air from the burner circulates around the entire exterior of the oven cavity to heat the same before being admitted through the fan into the interior thereof.
This design then has the disadvantage of restricting rack space due to the external heated air circulation pattern. Furthermore, the heated air circulating around the oven will lose heat content before entering the cavity to be circulated around the food to be cooked. Heated walls then will transmit that heat primarily by radiation to the food to be cooked whereas the primary cooking will occur by the convection currents circulating through the cavity, in contrast to those currents circulating around the exterior of the cavity.
Other types of fan arrangements in convection ovens are shown, for example, in U.S. Pat. Nos. 4,926,837 and 5,309,981.